When Hiccup finds a coffin at sea, he opens it to discover a riddle that will lead to the treasure of Grimbeard the Ghastly, the world's greatest pirate and Hiccup's ancestor. Setting out on a treasure hunt, Hiccup and his friends must master the art of swordfighting! How else will they escape an island of homicidal dragons, defeat a boatload of Viking pirates, and survive a dirty double cross?